The present invention relates to an improved process for consolidating geological formations, this process being in particular applicable to oil and gas reservoirs, to prevent sand from flowing into a well traversing unconsolidated, or insufficiently consolidated sand formations.
More generally this process can be used to locally consolidate permeable formations. Various methods have already been proposed to prevent sand from flowing into new boreholes, or to treat wells liable to be subjected to sand flowing during exploitation of oil or gas deposits.
A first type of method consists in maintaining the sand by mechanical means, using artificial screens with calibrated apertures, or packs of gravels having a well-defined size distribution, depending on the size of the sand particles or grains of the geological formation traversed by the borehole. Such a method is very often applied to new wells, but is difficult to put into operation.
A second type of method consists in injecting into the geological formation a liquid resin which, by polymerization, creates a bond between the sand grains. The efficiency of a chemical method of this second type is uncertain, since the reacton of polymerization of the injected resin depends essentially on the conditions prevailing in the borehole at the level of the formation and on the characteristics of the latter. Thus such a method does not permit control of the extent of the chemical reaction.
There is thus the risk either of an insufficient consolidation of the formation if the degree of polymerization of the resin is not sufficient, or of an excessive reduction of the permeability of the geological formation, or even of complete plugging thereof, if a too large amount of polymer is retained in some of the pores of the formation.
U.S. Pat. No. 3,388,743 discloses a consolidation method wherein injection of a drying oil into formations surrounding a borehole is followed by the injection of an oxidizing gas.
The partially oxidized oil constitutes a good binding material for the sand particles. By using an oxidizing catalyst, such as lead or cobalt naphthenate it is possible to shorten the time required for oxidizing the oil.
However the consolidation obtained by application of this method is generally insufficient for the intended purpose.
French Pat. No. 1,409,599 also describes a process for consolidating the grounds, wherein these grounds are treated by oily polymers containing siccative or drying catalysts which are hardened by air drying on the surface of the ground to be consolidated.
This treatment, which produces hard impermeable ground masses, is however unsuitable for consolidating subterranean formations whose permeability must be preserved.
U.S. Pat. No. 2,863,510 describes a process wherein oxidizable organic compounds are introduced into geological formations; however this process is adapted to the production of hydrocarbons by underground combustion.
German Pat. No. 2,343,021 and U.S. Pat. No. 3,941,191 describe a process for consolidating geological formations by means of solidifying agents, using combustion promoters as well as combustion activators, the oxidation being performed by injecting an oxygen-containing gas.
However this proccess suffers from the drawback of requiring combustion promoters and is really efficient only if the geological formation is preheated.